Integrated circuits typically include various active and passive circuit elements which have been integrated into a piece of semiconductor material, often referred to as a die. The die may, in turn, be fully or partially encapsulated into a package, which often includes a ceramic or plastic substrate although other materials may be used. The package mechanically supports and protects the die which is often relatively fragile.
These packages are usually attached to a printed circuit board through their second level interconnects, which often are pins, balls or other connectors arranged along the exterior of the package. The package may be attached directly to the printed circuit board, often by soldering or other connection techniques. In some applications, the package may not connect directly to the printed circuit board. Instead, an interposer or socket or other device may provide an intermediate connection between the package and the printed circuit board.
Conductors of the package typically provide separate electrical connection terminals between the printed circuit board (or interposer or socket), and the various inputs and outputs of the integrated circuit or circuits within the package. An integrated circuit die often has electrical connectors such as solder bumps to mechanically and electrically connect the integrated circuit die to the package substrate. In this manner, an electronic system can be formed by connecting various integrated circuit packages to a printed circuit board. In this regard the packaged can be viewed as a space transformer, transforming the very fine pitches on the order of 10s of microns on the silicon die side to 100s of microns on the printed circuit board side.
Inductors are used in numerous microelectronic applications, such as high frequency circuits, low-noise and power amplifiers, mixers, voltage-controlled-oscillators (VCO), power transfer and noise matching networks, circuits for reducing electromagnetic interference (EMI), power converters (including direct-current to direct-current, alternating-current to alternating-current, direct-current to alternating current, and alternating-current to direct-current converters) for the distribution of power to circuits, and clocking circuits. In addition, other applications include radio frequency (RF) circuits such as are used in a myriad of wireless devices like cellular telephones, wireless modems, and other types of communications equipment.
An inductor is a conductor which is shaped in a manner which can store energy in a magnetic field adjacent to the conductor and/or partially inside the conductor. Various designs of inductors are known. Common shapes for inductors include planar and multilayer spirals, helixes and serpentine shapes. Thus, an inductor typically has one or more “turns” which can concentrate the flux of the magnetic field induced by current flowing through each turn of the conductor in a central area defined by the inductor turns. This central area is typically referred to as the inductor core. The inductance of the inductor may often be increased by positioning magnetically permeable materials such as iron, steel, or other ferrites within the inductor core or within other areas adjacent to the conductor and within the magnetic fields so that the inductor and the magnetically permeable material are magnetically coupled to each other. The inductance may also be increased by increasing the number of turns of the inductor.
In some applications, discrete inductors are attached directly to a printed circuit board. In other applications, inductors have been embedded into printed circuit boards or integrated into or onto the semiconductor substrate of an integrated circuit die. In die substrates having multiple metal interconnect layers, a turn of an inductor may be embedded into each layer. In yet other applications, inductors have been embedded into the substrate of a package supporting and protecting an integrated circuit die. In package substrates having multiple built-up layers, a turn of an inductor may be embedded into each layer.